1. Field of the Invention
The invention relates to a process for the hydroformylation of higher olefins in the presence of an unmodified cobalt carbonyl complex by maintaining a aqueous bottom phase in the hydroformylation reactor.
2. Discussion of the Background
It is known that higher alcohols, in particular those having from 6 to 25 carbon atoms, can be prepared by catalytic hydroformylation (oxo process) of the olefins having one less carbon atom and subsequent catalytic hydrogenation of the aldehyde- and alcohol-containing reaction mixtures. They are used predominantly for the preparation of plasticizers and detergents. However, it is also possible to separate off aldehydes by distillation of the hydroformylation mixtures. These aldehydes can, for example, be utilized for preparing carboxylic acids.
The type of catalyst system and the optimum reaction conditions for the hydroformylation are dependent on the reactivity of the olefin used. The dependence of the reactivity of the olefin on this structure is described, for example, by J. Falbe, New Syntheses with Carbon Monoxide, Springer-Verlag, Berlin, Heidelberg, New York, 1980, page 95 ff. The differing reactivity of, in particular, the isomeric octenes is likewise known (B. L. Haymore, A. van Hasselt, R. Beck, Annals of the New York Acad. Sci., 415 (1983), pages 159-175).
Industrial olefin mixtures which are used as starting materials for the oxo process comprise olefin isomers having various structures and different degrees of branching, different positions of the double bond in the molecule and possibly also different numbers of carbon atoms. This applies particularly to olefin mixtures which have been formed by dimerization or trimerization or further oligomerization of C2-C5-olefins or other readily available higher olefins or by cooligomerization of the olefins mentioned. Examples of typical isomeric olefin mixtures which can be converted by means of rhodium-catalyzed or preferably cobalt-catalyzed hydroformylation into the corresponding aldehyde and alcohol mixtures are tripropenes and tetrapropenes and also dibutenes, tributenes and tetrabutenes.
If alcohols having a low degree of branching are wanted as hydroformylation product, the hydroformylation is advantageously carried out using unmodified cobalt catalysts. Compared to rhodium catalysts, cobalt catalysts give, starting from the same olefin mixture, higher yields of the particularly valuable straight-chain oxo products.
The hydroformylation of olefins using unmodified cobalt catalysts can, apart from the catalyst work-up, be carried out in one or more stages.
However, the known multistage processes for preparing oxo aldehydes in the presence of unmodified cobalt catalysts have a series of engineering disadvantages. Thus, the preparation of the cobalt catalyst required for the hydroformylation requires two technically complicated process steps: precarbonylation and catalyst extraction. Due to the mass transfer processes occurring in the two process steps: gas/liquid mass transfer in the precarbonylation and liquid/liquid mass transfer in the catalyst extraction, two separate pressure-rated apparatuses, for example, stirred vessels or packed columns, are necessary. The actual hydroformylation subsequently takes place in another separate pressure reactor.
The German patent application DE 196 54 340 describes a process in which precarbonylation, catalyst extraction and olefin hydroformylation are carried out in one reactor. Compared to the known multistate processes, this process has the advantages of a lower capital outlay and lower operating costs. However, it has the disadvantage that carrying out the single-stage process is quite difficult, since the substeps of the process, e.g. catalyst formation, extraction of the catalyst into the organic phase and hydroformylation, occurs simultaneously. An aqueous cobalt salt solution in which the catalyst is formed is present in the lower part of the reactor. The hydroformylation occurs mainly in the homogeneous organic phase. Water and cobalt compounds are continuously carried out from the reactor in the hydroformylation mixture leaving the reactor and the synthesis gas which is taken off, so that further quantities of cobalt compounds and water continually have to be introduced.
Although the single-stage process has been found to be useful in overall terms, fluctuations in conversion and selectivity occur during operation and continuous operation is disrupted by precipitation of cobalt compounds and/or metallic cobalt.
It is an object of the present invention to provide a single-stage process in which the above-mentioned difficulties during continuous operation are avoided and the target products are obtained in high yield and with high selectivity.
This and other objects have been achieved by the present invention the first embodiment which includes a process for the hydroformylation of an olefin, comprising:
reacting said olefin or a mixture of olefins in the presence of an unmodified cobalt catalyst in a single-stage process in a reactor at a temperature of from 100xc2x0 C. to 220xc2x0 C. and a pressure of from 100 bar to 400 bar, to obtain an aldehyde, an alcohol or a mixture thereof;
wherein an aqueous bottom phase and an organic phase are present in said reactor;
wherein the aqueous bottom phase is mixed with the organic phase;
wherein a concentration of said cobalt catalyst, calculated as metallic cobalt, in said aqueous bottom phase is in the range from 0.4 to 1.7% by mass based on a total weight of said aqueous bottom phase; and
wherein a level of the aqueous bottom phase in said reactor is kept constant during steady-state operation.